The present invention relates to a data transfer control device and an electronic instrument.
In recent years, a high-speed serial transfer interface such as low voltage differential signaling (LVDS) has attracted attention as an interface standard aiming at reducing EMI noise or the like. In such a high-speed serial transfer interface, data transfer is implemented by causing a transmitter circuit to transmit serialized data using differential signals and a receiver circuit to differentially amplify the differential signals (Japanese Patent Application Laid-open No. 2001-222249).
An ordinary portable telephone includes a first instrument section provided with buttons for inputting a telephone number or a character, a second instrument section provided with a main liquid crystal display (LCD), a sub LCD, or a camera, and a connection section such as a hinge which connects the first and second instrument sections. In this case, the number of interconnects passing through the connection section can be reduced by performing data transfer between a first substrate provided in the first instrument section and a second substrate provided in the second instrument section by serial transfer using serial signal lines. Therefore, a high-speed serial interface which can implement efficient serial transfer in the connection section has been demanded.
In such a high-speed serial interface, an idle state which is a state in which data is not transferred on a bus is defined. In IEEE1394 which is one of the high-speed serial interfaces, the right to exclusively access the bus is arbitrated among a plurality of nodes, and a node which wins the arbitration exclusively accesses the bus. Therefore, since the node which has lost the right to exclusively access the bus releases the bus, that node does not drive the serial signal lines in the idle period.
In PCI Express which has attracted attention as a high-speed serial interface for a personal computer, an idle code is output to the serial signal line in the idle period. However, the method of outputting the idle code in the idle period requires that an encoder circuit (code generation circuit) and a decoder circuit (code detection circuit) of a data transfer control device operate even in the idle period. In a personal computer which is the target of PCI Express, since a reduction of power consumption is not strongly demanded, a considerable problem does not occur even if the idle code is output in the idle period. However, a reduction of power consumption during standby is strongly demanded for a portable information device such as a portable telephone. Therefore, a data transfer control device which can reduce power consumption in the idle period is demanded.